The present invention relates to camera assemblies having automatic winding devices, and more particularly to a camera assembly having an automatic winding device with an electric motor as a drive source for performing film winding and shutter cocking operation.
It is known in the art to provide an automatic winding device for a photographic camera in the form of an attachment with a setscrew adapted to engage with a mating thread which is formed in the bottom wall of the camera housing in order to enable the camera to be supported by a tripod. This attachment accommodates an electric motor and a speed reduction gear mechanism, with a battery serving as the electrical power source, particularly when the camera is portable and capable of being carried about. However, the combined bulk and weight of the electric motor, the gear mechanism and the battery detract from the portability and ease of manipulation of the camera and make operation thereof difficult to perform. Although the performance characteristics of the electric motor and battery have recently been improved, since the driving torque necessary to effect shutter cocking and film winding remains considerable, a speed reduction mechanism is not yet indispensable to automatic operation of the camera. In order to insure that a continuous succession of frame exposures can be effected with highly accurate and reliable film feed and exposure control even with significant increase in frame frequency, it is required that the dimensions of the electric motor and the battery be increased. This requirement is, however, inconsistent with improving the compactness of the automatic winding device itself.
If the motor drive is housed at the bottom of the camera housing, it constitutes a heavy weight suspended downwardly from the camera, increasing the difficulty of maintaining the camera sufficiently stable without use of a support device such as a tripod. A conventional solution of this problem is to provide a hollow grip in fixedly-secured relation to the housing of the winding device so that the electric motor may be situated in the internal space of the grip with or without the battery. By grasping the grip, the user is able to hold the camera sufficiently stable to focus upon an object which it is desired to photograph.
Another problem of conventional motor driven winding devices is low efficiency in driving the electric motor. In general, the automatic winding process comprises the steps of detecting completion of advance of one frame of the film by a torque sensor, de-energizing the motor, and after completion of the next exposure, energizing the motor to initiate the next cycle of winding operation. Since the motor must be stopped rapidly and must then increase its speed rapidly at the start, while driving the speed reduction mechanism and the film winding mechanism, a large proportion of the electrical energy in the battery is consumed inefficiently by the inertia of these mechanisms.
To enhance the efficiency of the motor, it has been proposed to utilize an automatic winding device having an electromagnetic clutch associated with the motor. According to this proposal as applied in high-speed photography applications, the motor is maintained energized throughout a series of continuous frame exposures and operation of the electromagnetic clutch is controlled to start transmission therethrough of the motor drive, and to terminate transmission after completion of an exposure and after each cycle of winding operation. Thus, large power losses which might otherwise result from the inertia of moving parts of the mechanism during rapid speed increase or braking of the motor are eliminated.
However, the provision of the electromagnetic clutch causes an increase in the weight and bulk of the motor drive unit, and the amount of electrical energy consumed by the electromagnetic clutch is not negligible. Thus, other disadvantages arise because failure to make the motor drive unit as compact as possible will seriously detract from the ease of operation of the camera.